Field of the Invention
The present invention relates to a focus adjustment apparatus a focus adjustment method, and a program for performing the focus adjustment method. In particular, the present invention relates to a focus adjustment apparatus and a focus adjustment method which perform a focus adjustment by an image pickup place phase difference or (auto focus) method, a program which performs the focus adjustment method, and an image pickup apparatus to which the focus adjustment apparatus and method are applicable.
Description of the Related Art
Recently, in an image pickup apparatus which is typified by a single-lens reflect camera, the weight of a photographing method to be performed while a user is watching an LV (live view) screen has been highly increased. In this connection, various AF methods which have been proposed to be used for the image pickup apparatus mainly include a phase difference detection method and a contrast detection method.
In the phase difference detection method, light fluxes which passed through mutually different exit pupil areas in an image pickup optical system are imaged on a pair of line sensors for photometry, a defocus amount of the image pickup optical system is calculated by a phase difference of a pair of image signals obtained by the pair of line sensors, and an in-focus state is obtained by moving a focus lens by a movement amount corresponding to the calculated defocus amount (Japanese Patent Application Laid-Open No. H09-054242). However, since the optical path to the imaging element is blocked in the above phase difference detection method using the line sensors, this method basically makes the photographing performed while watching the LV screen difficult.
In the contrast detection method, an in-focus state is obtained by, while moving a focus lens, searching for the focus lens position at which a contrast evaluation value generated from an image signal obtained using an imaging element becomes maximum (Japanese Patent Application Laid-Open No. 2001-004914). Since the contrast detection method is suitable for AF in the LV photographing because the focusing is performed based on the image signal, this method is the best mainstream method in the LV photographing recently. However, in the contrast detection method, it is impossible to easily determine focus position and direction for obtaining an in-focus object. Consequently, in this method, there are cases where it takes a time for obtaining the in-focus state, the direction for the focusing is erroneously determined, and the focus position overreaches the in-focus position. These cases decrease focusing accuracy.
The recently demanded photographing performed while watching the LV screen is used for not only a still image but also a moving image. For this reason, when AF control is performed, in addition to responsiveness for quick focusing, accuracy is required in a focusing operation. In this connection, an AF method which can accurately perform the focusing at high speed in the LV photographing has been proposed recently. As an example of the AF method, there is an image pickup plane phase difference detection method by which the above phase difference detection method is performed on the imaging element plane (surface).
As one kind or the image pickup plane phase difference detection method, a method of simultaneously performing imaging and focus detection by performing pupil division of imaging pixels of an imaging element with a microlens and receiving a light flux from each divided pupil with a plurality of focus detection pixels has been proposed. In Japanese Patent Application Laid-Open No. 2001-083407, in one pixel (unit pixel), a photodiode which receives light collected by a microlens is divided, and thus light of a different pupil surface of an imaging lens is received by each photodiode. Therefore, by comparing the outputs of the two photodiodes, it is possible to perform the image pickup plane phase difference detection method. Consequently, by using the image pickup plane phase difference detection method, it is possible to perform AF using the phase difference detection method even in the LV photographing, and it is thus possible to accurately perform the focusing at high speed.
As one of objects for which it is difficult to perform AF, there is a perspective-conflict object which includes a plurality of objects respectively having different object distances in a ranging area (i.e., a distance measurement area). If the perspective-conflict object is photographed by the phase difference detection method or the image pickup plane phase difference detection method, as illustrated in FIGS. 15A and 15B, there is a problem that both near-side and far-side objects are out of focus and thus AF is completed with such out of focus. Japanese Patent Application Laid-Open No. H08-015603 proposes an AF method to be performed according to the phase difference detection. In this method, when it is determined that a perspective conflict occurs in objects, a ranging area is divided and the phase difference detection is again performed, and a defocus amount is calculated in the ranging area in which the perspective conflict does not occur.
However, as disclosed in Japanese Patent Application Laid-Open No. H08-015603, when the ranging area is divided based on the phase difference detection result and the phase difference detection is again performed, time that elapses before the completion of AF is prolonged by the amount of time necessary for repetition of the phase difference detection. Thus, a problem that responsiveness for AF deteriorates occurs. Moreover, in a case where objects respectively having different object distances exist above and below in a line sensor as illustrated in FIG. 16, when the proposed method is used, since a perspective conflict cannot be detected, focusing is performed with out of focus. As just described, in the case where the perspective-conflict objects exist in the divisional and vertical directions of the line sensor, it is impossible to improve problems.
The present invention, which has been completed in consideration of the above conventional problems, aims to achieve the focusing which is suitable for the perspective-conflict object in the AF control using the phase difference detection method.